An embodiment of the present invention relates to an image forming apparatus that eliminates problems such as rubbing marks caused by oozing of wax that occurs during the cooling of a fixing unit installed in an image forming apparatus using toners that include wax.
A fixing unit installed in an image forming apparatus is provided with a mechanism that carries out fixing by heating while nipping and conveying the image supporting material which is the transfer material having the transferred image on it using, for example, a heat roller as the fixing member and using, for example, a pressure roller as the pressing member that presses against and is in contact with the heat roller.
Further, related to such fixing units:
Firstly, regarding the edge part temperature rise of heating sections such as the heat roller in a fixing unit, at the time of fixing sheets with small sizes, although there is the problem that the fixing temperature of parts through which the paper does not pass rises excessively, the technique of forced air cooling selectively the edge parts of the fixing apparatus is present as a conventional technology, as disclosed in Japanese Unexamined Patent Application Laid Open No. Hei 4-51179 and Japanese Unexamined Patent Application Laid Open No. Hei 5-107983.
Secondly, when using toners that include wax, regarding the conveyance rubbing marks occurring on the downstream side of the fixing unit, although wax oozes out on the surface of a fixed image of a toner that includes wax, there is the trend of the glossiness of the wax increasing if cooled suddenly near the crystallization temperature and of the glossiness of the wax decreasing if cooled slowly. As a consequence, the image rubs against conveying rollers and guiding members on the downstream side of the fixing unit, and rubbing marks remain upon sudden cooling. In order to prevent this, although there is the technique, as disclosed in Japanese Unexamined Patent Application Laid Open No. 2003-20149, of installing the roller pairs at a separation on the downstream side of fixing, paper rubs against the rollers due to the behavior of the sheets and marks are formed on them. In addition, since conveying force cannot be generated, there will be limitations on the conveying path. In view of this, air is blown and slow cooling (or fast cooling) is done immediately after fixing.
Patent Document 1: Japanese Unexamined Patent Application Laid Open No. Hei 4-51179.
Patent Document 2: Japanese Unexamined Patent Application Laid Open No. Hei 5-107983.
Patent Document 3: Japanese Unexamined Patent Application Laid Open No. 2003-20149.
In this manner, in an image forming apparatus using toners that include wax, in order to solve the above problems, at least two systems of air blowing unit were required in a conventional fixing unit, and hence the apparatus became large in size and higher in cost.